1. Field of the Invention
The present invention relates to coaxial connectors mountable on an end of a coaxial cable having a central conductor and an exterior conductor.
All the materials which are used in fabricating coaxial cables, the metals as well as the plastics, are non-elastic materials. The fixing onto the cable, the sealing and the electric contacts are functions which are realised by forces between the elements of the cable and the elements of the connector during the mounting of the latter on the cable. The majority of existing connectors use rigid elements for applying the necessary forces for realising one or more of the functions, which leads to a material flow which consists of a cold deformation for eliminating mechanical stress. The forces diminish to an extent which is insufficient for the respective function. An other problem of existing connectors is the use of an internal threaded part for holding the exterior conductor of the cable. Such internal threaded part creates grooves in the outer conductor which can break the connection. For certain cables with a fragile exterior conductor, for example a braid of metallic strands, rigid contact systems are used which press the fragile conductor against the dielectric on the interior thereof, with the same risk of possible breakage. Furthermore, the deformation of the cross-section of the cable by this type of gripping can modify the impedance of the cables and disturb the transmission of the signal. All these disadvantages of rigid contact elements are increased in the field as a result of temperature variations and vibrations.
2. The Prior Art
From EP-A-897 202 a coaxial connector is known, comprising a head portion having a recess which has one end formed with a first ring surface for establishing a contact from inside with an end zone of an outer cable conductor of a coaxial cable, and a restraint for the coaxial cable. The restraint is formed by a clamp bushing having a head portion side end formed with a second ring surface for clamping the end zone of the outer cable conductor from outside, and a pressure-applying member enclosing the cable and fastened to the head portion for forcing the clamp bushing in the axial direction against the first ring surface and to thereby clamp the end zone of the outer cable conductor between the first and second ring surfaces. At least one of the ring surfaces is formed with at least one annular bead which projects in the direction of a respective area of the end zone of the outer cable conductor and is defined by a height of approximately 5 to 30% of a wall thickness of the outer cable conductor. Upon tightening of the connector around the cable, this annular bead causes a plastic deformation of the outer conductor.
The coaxial connector known from EP-A-897 202 however has the disadvantage that the electrical contact between the outer cable conductor and the head portion may deteriorate in time.
It is a first aim of this invention to provide a coaxial connector in which the deterioration in time of the electrical contact with the outer cable conductor can be reduced.
It is a second aim of the invention to provide a coaxial connector with enhanced cable retention.
It is a third aim of the invention to provide a coaxial connector with an enhanced seal against penetration of moisture.